Amnesty International called Wednesday for an "immediate and unconditional" release of a new batch of political prisoners rounded up in Syria, including aging communist leader Riad Turk.

"Syrian authorities should initiate an irreversible break with the heavy legacy of human rights violations, starting by the immediate and unconditional release of all recently detained prisoners of conscience," it said.

Ten Syrian opposition figures, including MPs Riad Seif and Maamun al-Homsi and economist Aref Dalila, have been held for the past month. Most of them are accused of working "to modify the constitution and denigrate the state".

Amnesty hoped the reported "transfer in July and August of around 500 prisoners from Tadmor military prison" signaled "the first step towards redressing all violations inflicted on the prisoners over the years".

"Every aspect of life in Tadmor prison [in Palmyra, or Tadmur, central Syria] is a dehumanizing experience," said the London-based prisoners' rights group. "The level of brutality endured by prisoners in this prison is shocking."

Amnesty warned in a statement received in Nicosia that "no political or economic reforms in Syria will be possible unless priority is given to human rights protection and promotion."

The Paris-based Arab Committee on Human Rights (ACHR) reported at the start of September that Tadmor prison would likely be closed later in the year.

The closure would "be a positive sign in marking the end of a stage [dominated] by repression," it said.

President Bashar al-Assad granted amnesty to around 600 political prisoners last November, when another prison was closed and transformed into a hospital.

Rights groups estimate between 700 and 800 political prisoners are being held in Syria -- NICOSIA (AFP)